A custom-made mRNA cancer shot cut the risk of melanoma coming back or death by 42% in a large trial. Moderna and Merck shared the results Thursday, according to Ars Technica, the Guardian and Time.

The vaccine, intismeran, was given with the cancer drug Keytruda, also called pembrolizumab, the outlets reported. It was compared with Keytruda alone over two years, they said.

The late-stage trial included 1,137 patients whose melanoma had been removed by surgery, Ars Technica and the Guardian reported. Melanoma is the deadliest kind of skin cancer, Ars Technica said.

After two years, 82% of patients who got the vaccine were alive without the cancer returning, the Guardian reported. That compared with 70% of those who got Keytruda alone, it said.

Each vaccine is made for one patient, the outlets reported. It targets up to 34 mutations found in that patient's cancer, Ars Technica and the Guardian said.

The firms put out the main results early after a news site broke an embargo, Ars Technica reported. The results will be presented at a cancer meeting in Madrid on October 24, Time said.

The results have been accepted by the New England Journal of Medicine, Ars Technica and the Guardian reported.

The firms are already in talks with drug regulators, Ars Technica said.

"mRNA has the potential to fundamentally change how we treat cancer," Moderna CEO Stéphane Bancel said, according to Ars Technica.

An outside researcher said the shot would not help everyone with melanoma, the Guardian reported. "A significant portion do not respond to the vaccine in the first instance," she said, according to the Guardian.

What we know: The vaccine plus Keytruda lowered the risk of melanoma returning or death by 42%.
What we don't: When regulators might approve it, and how it will do over a longer time.